Laser absorption spectroscopy system and method for discrimination of a first and a second gas

ABSTRACT

A system and method to discriminate between a first preselected gas and at least one other preselected gas use of an absorption spectroscopy analyzer that includes a Herriott cell and a temperature sensitive light source. The light source operates at a temperature that emits a beam at a wavelength that corresponds to high absorption by a first preselected gas. When a predetermined level of this gas is detected in a gas sample, the analyzer changes the operating temperature of the light source to emit a beam at a wavelength that corresponds to high absorption by a second preselected gas. The second preselected gas can be a different isotope of the first preselected gas.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/378,994, filed Aug. 24, 2016, entitled “LASER ABSORPTIONSPECTROSCOPY SYSTEM AND METHOD FOR DISCRIMINATION OF A FIRST AND ASECOND GAS,” which is hereby incorporated by reference in its entiretyand for all purposes.

FIELD

The present disclosure relates generally to gas detection and analysis.In particular, the invention relates to portable laser absorptionspectroscopy systems and methods used to distinguish between two or moredifferent types of gas, such as during a leak survey.

BACKGROUND

A known and successful system for detecting small quantities of gas inthe environment is by the use of absorption spectroscopy (see U.S. Pat.No. 7,352,463 B2 to Bounaix, hereby incorporated by reference herein andincluded herein as Appendix A) and portable analyzers that incorporatethis technique in combination with a Herriott cell are commerciallyavailable (see GAZOMAT™ INSPECTRA® natural gas leak portable analyzer).By this technique, a light beam of a selected frequency that is highlyabsorbed by the particular gas for which the instrument is designed ispassed through a sample of the gas. The rate of absorption of the lightbeam is used as an indicator of the level of concentration of the gas inthe sample. To increase the light beam's length of travel through thegas, the Herriot (multi-path) cell is used.

The particular gas can be methane, butane, propane, ethane, oxygen,hydrogen, nitrogen, water vapor, hydrogen fluoride, hydrogen chloride,hydrogen bromide, hydrogen sulfide, ammonia, carbon monoxide, carbondioxide, nitrogen oxide, nitrogen dioxide, sulfur hexafluoride, oranother gas of interest. For example, the level of concentration ofmethane in a gas sample can be determined by initiating a light beam ata frequency that is highly absorbed by methane and passing the beamthrough the gas sample. To determine whether the methane is from anatural gas or a biogas source requires further discrimination.

Discrimination of natural gas and biogas is accomplished using eithergas chromatography systems or cavity ring-down spectroscopy (“CRDS”).Gas chromatography involves a long response time, is not very sensitive,and requires regular calibration. CRDS is expensive and can only be usedwith a leak survey car.

A need exists for an absorption spectroscopy system and method that candetect a first gas, like methane, and then immediately shift to detecttwo or more isotopes of that gas or detect an entirely different secondgas.

SUMMARY

The systems and methods of this disclosure each have several innovativeaspects, no single one of which is solely responsible for its desirableattributes. Without limiting the scope as expressed by the claims thatfollow, its more prominent features will now be discussed briefly.

In some embodiments, a method of measuring a concentration in anenvironment of at least a first preselected gas and a second preselectedgas is described. The method may include continuously moving a stream ofa sample gas from the environment through a confined testing area withina detecting instrument, energizing a light source of the detectinginstrument at a first operating temperature to produce a light beam at afirst preselected wavelength for absorption by the first preselectedgas, measuring the absorption of the light beam at the first preselectedwavelength to provide an indication of a concentration of the firstpreselected gas within the sample gas, energizing the light source at asecond operating temperature to produce a light beam at a secondpreselected wavelength for absorption by the second preselected gas, andmeasuring the absorption of the light beam at the second preselectedwavelength to provide an indication of a concentration of the secondpreselected gas within the sample gas. As noted in further detail below,adjustments in operating temperature of a light source may beaccomplished by energizing the light source (e.g., adjusting currentlevel provided to the light source) to the desired operating temperatureand/or activating a heating or cooling element to adjust temperature ofthe light source to the desired operating temperature.

At least one of the first and second preselected gases can be selectedfrom methane (CH₄), ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀),oxygen (O₂), hydrogen (H₂), nitrogen (N), water (H₂O), hydrogen fluoride(HF), hydrogen chloride (HCl), hydrogen bromide (HBr), hydrogen sulfide(H₂S), ammoniac (NH₃), ammonia (NH₄), carbon monoxide (CO), carbondioxide (CO₂), nitrogen monoxide (NO), nitrogen dioxide (NO₂), sulfurhexafluoride (SF₆), tetrahydrothiophene (C₄H₈S), and tert-butylmercaptan (C₄H₁₀S).

The second preselected gas can be an isotopologue of the firstpreselected gas. The first preselected gas and the second preselectedgas can be isotopologues of methane.

The light source can be configured to transition between the firstoperating temperature and the second operating temperature in less than10 seconds. The light source can be a laser diode. The light source canbe a light emitting diode. The absorption of the light beam at the firstpreselected wavelength and the absorption of the light beam at thesecond preselected wavelength can be measured at a photodetector.

The method can further comprise energizing an operating temperature ofthe photodetector. The operating temperature of the photodetector can becontrolled based on at least one of the first and second operatingtemperatures. The detecting instrument can further include a multi-passcell.

The light source can be energized at the second operating temperaturebased at least in part on the indication of the concentration of thefirst preselected gas. The light source can be energized at the secondoperating temperature responsive to the indication of the concentrationof the first preselected gas exceeding a predetermined threshold.

In another embodiment, a method of measuring a concentration in anenvironment of at least a first preselected gas and a second preselectedgas is described. In this embodiment, the method may includecontinuously moving a stream of a sample gas from the environmentthrough a confined testing area within a detecting instrument,energizing a light source of the detecting instrument to produce a lightbeam at a wavelength that corresponds to an absorption line of a gas,and energizing a photodetector at a first operating temperature todetect absorption of the light beam by the first preselected gas.

The method can further include energizing the photodetector at a secondoperating temperature to detect absorption of the light beam by thesecond preselected gas and measuring the absorption of the light beam toprovide an indication of a concentration of the second preselected gasat the preselected wavelength. The method can further include energizingthe light source at a first operating temperature to produce a lightbeam at a preselected wavelength for absorption by the first preselectedgas. The method can further include energizing the light source at asecond operating temperature to produce a light beam at a preselectedwavelength for absorption by the second gas.

In some embodiments a method of measuring a concentration in anenvironment of a preselected gas is described. In this embodiment, themethod may include continuously moving a stream of a sample gas from theenvironment through a confined testing area within a detectinginstrument, energizing a light source of the detecting instrument toproduce a light beam at a wavelength that corresponds to an absorptionline of a reference gas, energizing the light source at a firstoperating temperature to produce a light beam at a preselectedwavelength for absorption by a first preselected gas, the preselectedwavelength being a different wavelength than the wavelengthcorresponding to the absorption line of the reference gas, and measuringthe absorption of the light beam to provide an indication of aconcentration of the first preselected gas at the preselectedwavelength.

The method can further include energizing the light source at a secondoperating temperature to produce a light beam at a preselectedwavelength for absorption by a second preselected gas, and measuring theabsorption of the light beam to provide an indication of a concentrationof the second preselected gas at the preselected wavelength.

In some embodiments, an absorption spectroscopy system and method todiscriminate between at least a first and a second gas, or between atleast a first isotope and a second isotope of a same gas, changes theworking or operating temperature of the light beam's source between thatof a first light beam of a selected frequency that is highly absorbed bythe first gas and that of a second light beam of selected frequency thatis highly absorbed by the second gas. Preferably, the system and methodmake use of a detection instrument that includes a Herriott (multi-pass)cell.

In some embodiments of the system and method, a stream of sample gas iscontinuously moved from the environment through a confined testing arealocated with the detection instrument; a light source is energized toemit a light beam in a range of frequencies that correspond to anabsorption line of some gas (that is to be detected); the operatingtemperature of the light source is then energized to produce a lightbeam at a preselected frequency for absorption by a preselected gas, theabsorption is measured by way of a photodetector (or its equivalent) toprovide an indication of the concentration of the preselected gas at thepreselected frequency, and the operating temperature of the light sourceis then energized to produce a light beam at a preselected frequency forabsorption by another preselected gas. The light source can be a laserdiode or a light emitting diode (“LED”).

The change in operating temperature, which preferably takes less than 10seconds, can be a conditional shift, for example, dependent on whetherthe first gas is detected, a cyclical or regularly occurring shift, oran operator-determined shift. The operating temperature also can beshifted to detect a third preselected gas and then another (and so on).The preselected gas can be isotopes of the same group of gas.

In some embodiments, the operating temperature of a photodetectorarranged to receive the light beam can be managed in correlation withthat of the light source to increase the sensitivity of detection forthe preselected gas. Optionally, the operating temperature of thephotodetector can be changed independent of that of the light source.

In some embodiments, the various systems discussed herein may perform amethod including moving a stream of sample gas from the environmentthrough a confined testing area within a detecting instrument (e.g.,continuously pushing or pulling air through the testing area);energizing a light source at a first operating temperature to produce afirst light beam at a frequency that corresponds to a high degree ofabsorption by a first preselected gas; splitting the first light beaminto multiple components (e.g., three or more); passing a firstcomponent of the first light beam to a first photo detector forproviding a first electrical signal indicative of the intensity of thefirst light beam; passing a second component of the first light beammultiple times through the confined testing area and then to a secondphoto detector for providing a second electrical signal indicative of aconcentration measurement corresponding to a lower concentration level;passing a third component of the first light beam over a reduced lengthpath through the confined testing area and then to a third photodetector for providing a third electrical signal indicative of aconcentration measurement corresponding to a higher concentration level;and using the first, second, and third electrical signals fordetermining the concentration level of the first preselected gas in thestream of sample gas. This embodiments may further include energizingthe light source at a second operating temperature to produce a secondlight beam at a frequency that corresponds to a high degree ofabsorption by a second preselected gas; splitting the second light beaminto multiple components; passing a first component of the second lightbeam to the first photo detector for providing a first electrical signalindicative of the intensity of the second light beam; passing a secondcomponent of the second light beam multiple times through the confinedtesting area and then to the second photo detector for providing asecond electrical signal indicative of a concentration measurementcorresponding to a lower concentration level; passing a third componentof the second light beam over a reduced length path through the confinedtesting area and then to the third photo detector for providing a thirdelectrical signal indicative of a concentration measurementcorresponding to a higher concentration level; and using the first,second, and third electrical signals for determining the concentrationlevel of the second preselected gas in the stream of sample gas.

Objectives of this invention including providing an absorptionspectroscopy system and method that can automatically shift betweendetection of a first preselected gas and at least one other preselectedgas or shift between detection of a first isotope and at least one otherisotope of a same gas.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-mentioned aspects, as well as other features, aspects, andadvantages of the present technology will now be described in connectionwith various implementations, with reference to the accompanyingdrawings. The illustrated implementations are merely examples and arenot intended to be limiting. Throughout the drawings, similar symbolstypically identify similar components, unless context dictatesotherwise.

FIG. 1 is a schematic of the basic elements of one embodiment of anabsorption spectroscopy analyzer.

FIG. 2 is another schematic of an example embodiment of the analyzer ofFIG. 1.

FIG. 3 is a flow diagram of an example embodiment of a method todiscriminate between a first and a second preselected gas or betweenpreselected isotopes of the same gas.

FIG. 4 is a portion of the absorption spectra of a first gas and asecond gas in accordance with an exemplary embodiment.

FIG. 5 is a flow diagram of an exemplary method of discriminationbetween a first and a second isotope of a gas.

NUMBERING AND ELEMENTS USED IN THE DRAWINGS AND DETAILED DESCRIPTION

The following reference numerals are used in FIGS. 1 and 2 andaccompanying description.

-   -   10 Herriott cell (confined testing area of detection instrument        or analyzer)    -   12 Light beam    -   12A Portion of 12 entering 10    -   12B Portion of 12 reflected away from 10    -   14 Light beam source (laser diode or light emitting diode or        their equivalent)    -   16 Temperature regulating system    -   20 Inlet tube    -   24 Outlet tube    -   28 Discharge tube    -   30 Aperture or window in 44    -   31 Reference cell    -   32 First photodetector    -   34 Conductor    -   36 Amplifier    -   38 Analog-to-digital convertor    -   40 Conductor    -   42 Microprocessor    -   44 First mirror    -   46 Second mirror    -   48 Aperture or window in 46    -   50 Exit beam (long path)    -   52 Third photodetector (high sensitivity)    -   54 Conductor    -   56 Amplifier    -   58 Analog-to-digital convertor    -   60 Conductor    -   62 Exit beam (short path)    -   64 Second photodetector (low sensitivity)    -   66 Conductor    -   68 Amplifier    -   70 Analog-to-digital convertor    -   72 Conductor

DETAILED DESCRIPTION

The following description is directed to certain implementations for thepurpose of describing the innovative aspects of this disclosure.However, a person having ordinary skill in the art will readilyrecognize that the teachings herein can be applied in a multitude ofdifferent ways. The described implementations may be implemented in anygas detection and/or analysis system.

In some embodiments, a portable absorption spectroscopy systemautomatically discriminates between detection of a first preselected gasand a second preselected gas by changing the operating temperature“T_(op)” of a light source between a first operating temperatureT_(op(1)) to a second operating temperature T_(op(2)). When at the firstoperating temperature T_(op(1)), the light source emits a first lightbeam of a selected frequency “f₍₁₎” that is highly absorbed by the firstpreselected gas. When at the second operating temperature T_(op(2)), thelight source emits a second light beam of a selected frequency “f(2)”that is highly absorbed by the second preselected gas. Light offrequency f₍₁₎ can equally be characterized as having a wavelength λ₍₁₎,where λ₍₁₎=c/f₍₁₎. Similarly, light of frequency f₍₂₎ can equally becharacterized as having a wavelength λ₍₂₎, where λ₍₂₎=C/f₍₂₎.

In certain embodiments, the shift in frequency or wavelength relative tothis temperature shift can be characterized by:

dλ/dT=(0.1 nm)/° C.  (Eq. 1),

where dλ/dT is the rate of change in the emitted wavelength with respectto the temperature of the light source. In various embodiments, the rateof change dλ/dT may be greater or less than 0.1 nm/° C., depending onthe electrical and/or thermal properties of each light beam source. Inaddition, the rate of change dλ/dT of an individual light beam sourcemay vary across the range of operating temperatures. Thus, one or morelookup tables may be generated based on experimentally determinedoperating temperatures associated with known wavelengths.

The shift from the first operating temperature T_(op(1)) to the secondoperating temperature T_(op(2)) can be a conditional shift, for example,occurring when the first gas is detected at or above a predetermineddetection limit (see e.g. FIG. 3). A return from the second operatingtemperature T_(op(2)) to the first operating temperature T_(op(1)) canalso be a conditional shift, for example, occurring after the second gasis detected at or above its predetermined detection limit or after apredetermined period of time during which no second gas is detected.Preferably, the time required to shift between the first and secondoperating temperatures, and therefore between the different frequenciesor wavelengths, is 10 seconds or less, more preferably a few seconds orless and, even more preferably, no more than 2 seconds.

The first preselected gas can be methane, butane, propane, ethane,oxygen, hydrogen, nitrogen, water vapor, hydrogen fluoride, hydrogenchloride, hydrogen boride, hydrogen sulfide, ammonia, carbon monoxide,carbon dioxide, nitrogen oxide, nitrogen dioxide, sulfur hexafluoride,tetrahydrothiophene, tert-butyl mercaptan, or another gas of interest.The second preselected gas can be selected from that same group ofgases, being either an entirely different gas than the first preselectedgas (e.g. the first gas being CH₄, the second gas being C₂H₆) or adifferent isotope than that of the first preselected gas (e.g. the firstgas being ¹²CH₄, the second gas being ¹³CH₄).

A laser absorption spectroscopy analyzer like that disclosed in U.S.Pat. No. 7,352,463 B2 to Bounaix, incorporated herein by reference, canbe modified so that the analyzer shifts the operating temperature of thelight beam's light source. In this way, discrimination between the twogases or isotopes of the same gas occurs within a single setup.

FIG. 1 is a block diagram of an example laser absorption spectroscopyanalyzer. In this example, the analyzer includes a cell 10 that will bedescribed in detail subsequently, and that provides an environment inwhich a light beam 12 passes through a gas sample and in whichabsorption of the light beam is measured.

In the various embodiments discussed herein, a light beam is provided bya laser diode, in which case light beam 12 is a laser light beam.However, the various systems and methods discussed herein can bepracticed using a light source that provides a non-coherent light beam.An example of a non-coherent light source is a light emitting diode(LED). A laser diode provides a coherent light beam that is a beam ofsubstantially uniform frequency light having the characteristic that thelaser light beam does not disperse to the same extent as a non-coherentlight beam. The use of a laser beam, such as produced by a laser diode,is advantageous, but the use of a laser diode is not indispensable.However, laser diodes are expensive compared to LEDs. In someapplications, LEDs work satisfactorily. As used throughout thisdescription, “laser beam” or “laser diode” are inclusive of “light beam”or “LED.”

Supported to cell 10 is a structure that includes a laser diode 14 that,when energized, produces laser beam 12. Laser diodes of the typerepresented by 14 are temperature sensitive. That is, the frequency ofthe laser light produced by diode 14 varies according to the temperatureof the diode. For measurement accuracy it is important that thefrequency of laser beam 12 be controlled within a fairly narrow range,which in turn means that the temperature of laser diode 14 must becontrolled. For this purpose, a temperature regulating system generallyindicated by the block 16 is employed and will be described in detailsubsequently.

The analyzer functions by moving laser beam 12 through a gas sample anddetermining the level of concentration of a selected gas in the gassample by measuring absorption of the laser beam. This technology isgenerally referred to as “laser absorption spectroscopy.” Cell 10,including the components secured in relation to it, provide a tunablelaser diode absorption spectroscope. Flow channels are provided by whicha gas sample is moved through cell 10. Sample gas is taken in through aninlet 18 in inlet tube 20 and flows through filter 22 into the interiorof cell 10. The gas flows through cell 10 to an outlet tube 24 thatconnects with temperature regulating system 16. In this example, gas ismoved through the system by means of a gas pump 26 to a discharge tube28 by which the gas sample is returned to the environment.

In this embodiment, laser beam 12 passes through a window. A portion ofthe beam passes through an aperture 30 in a first mirror 44. The number12A represents the first pass of the beam internally of cell 10. Aportion of laser beam 12 is reflected by the window, the reflected beambeing indicated by the numeral 12B. A photo detector 32 is placed toreceive the interception of reflected beam 12B and provides anelectrical signal that is representative of the intensity of laser beam12. The electrical signal from photo detector 32 is conveyed byconductor 34 to an amplifier 36 that feeds into an analog to digitalconverter circuit 38 that provides a referenced digital input overconductor 40 that feeds into a microcontroller 42.

In many of the examples discussed herein, cell 10 is of a type generallyknown as a “Herriott” cell. This name is derived from the inventor of acell that employs opposed mirrors that reflect a light beam back andforth between them so that a relatively long path can be obtained in arelatively shorter length instrument, and in which the path is in acircular pattern. While generally of the “Herriott” type, cell 10 hasmany improvements and innovations as will be described subsequently indetail. Furthermore, other types of detection cells may be used.

In the example of FIG. 2, cell 10 employs a first mirror 44 and anopposed second mirror 46. A small aperture 30 is provided in firstmirror 44 through which the laser beam passes and forms beam 12A withinthe cell that first impacts second mirror 46. Beam 12A is reflectedsequentially between mirrors 44 and 46 a number of times before exitingsecond mirror 46 through a small aperture 48. The exit beam 50 impingeson a second photo detector 52 that provides a signal on conductor 54feeding an amplifier circuit 56 that feeds a second analog to digitalconverter 58 that provides a digital signal on conductor 60 leading tomicrocontroller 42.

As noted above, the methods and systems disclosed herein may be used todetect selected gasses such as methane, butane, propane, ethane, oxygen,hydrogen, nitrogen, H2O, hydrogen fluoride, hydrogen chloride, hydrogenboride, hydrogen sulfide, ammonia, CO, CO2, NO, NO2 and SF6. The systemcan be adapted to detect different selected gases by changing out thelaser diode to one that produces the frequency of light most readilyabsorbed by the gas of interest. When a light emitting diode (ratherthan a laser diode) is used, the broader spectrum of light produced byit can detect more different gases but usually at higher concentrations.In some implementations, the systems disclosed herein will be describedin the context of detecting methane gas, since methane is the basiccomponent of natural gas and most manufactured fuel gasses. If a leakoccurs in a gas distribution system, it can usually be located bydetecting the presence of methane. Therefore, cell 10 may employ a laserdiode 14 that produces a beam characterized by a frequency thatcorresponds to a high degree of absorption by methane. Sample gas thatis drawn in through inlet 18 and flows by way of inlet tube 20 into andthrough cell 10 absorbs, that is, decreases the intensity of light beam12A in proportion to the quantity of methane contained in the samplegas.

In this example, light beam 50 passes out aperture 48 in second mirror46 after having been reflected many times between mirrors 44 and 46.Undergoing multiple reflections from the time beam 12A enters cell 10until it exits through aperture 48 means that the beam has traversed arelatively long path equal to many times the length of cell 10 which inturn means that ample provision has been made for absorption of thelight beam by the presence of methane in the gas sampler.

By comparing the intensity of the signal on conductor 34 with that onconductor 54 the concentration of methane in the sample gas passingthrough cell 10 can be ascertained. By accurate processing withinmicrocontroller 42 the amount of methane contained in the sample gaspassing through cell 10 can be determined with great accuracy and can beexpressed such as in parts per million. The presence of methane can bedetected at a sensitivity down to a few parts per million or even,ideally, to a sensitivity of one or less than one part per million.

As previously stated, beam 12 emanating from laser 14 passes through afirst aperture 30 in first mirror 44 to provide beam 12A within thecell. When the initial passage of laser beam 12A within cell 10encounters second mirror 46 most of the beam intensity is reflected backtowards first mirror 44 and subsequently repeatedly reflected betweenfirst mirror 44 and second mirror 46 to finally pass out through secondwindow 48 to form exit beam 50. However, when beam 12A strikes secondmirror 46 a small portion of the intensity of the beam passes throughthe mirror even though no aperture or window is provided since mostmirrored surfaces are not 100% reflective. The portion of light beam 12Athat passes through second mirror 46 provides a second exit beam 62 thatengages a third photo detector 64. This produces an electrical signal onconductor 66 passing to a third amplifier 68 that feeds an analog todigital converter 70 sending a digital signal by way of conductor 72 tomicrocontroller 42. The employment of two separate exit beams 50 and 62emanating from cell 10 to activate photo detectors 52 and 64 is animportant attribute of the invention herein. It is apparent that onlysignals appearing on conductors 40 and 60 feeding microcontroller 42 arerequired to measure low levels of concentration of methane in the gaspassing through cell 10. It is important to detect very small levels ofmethane in the sample gas, which is accomplished by employing a longlight path for the laser beam before the beam exits through window 48,however, this arrangement fails if a broader scale of methane detectionis required. If methane is present at a relatively high level in thesample gas passing through the cell the laser beam

Referring to FIG. 2, the major components of an absorption spectroscopysystem are illustrated that can be used to practice the discriminationmethod of FIG. 3. As described above with reference to FIG. 1, a gassample flows into a measurement cell where a light beam 12 passesthrough the gas sample. The sample exits by way of an outlet tube—whichcommunicates with a temperature regulating system 16—and the samplereturns to the environment. The light beam 12 is produced by atemperature sensitive light beam source 14 set to operate at a referenceor first operating temperature T_(op(1)) to produce a light beam 12 at afrequency or wavelength λ₍₁₎ that corresponds to a high degree ofabsorption by the first preselected gas:

$\begin{matrix}{\lambda_{ref} = {{\lambda_{(1)}\mspace{14mu} {for}\mspace{14mu} \frac{dA}{dI}} = {{0\mspace{14mu} {at}\mspace{14mu} I} = \frac{I_{\min} + I_{\max}}{2}}}} & \left( {{Eq}.\mspace{14mu} 2} \right)\end{matrix}$

where A is absorption and I is intensity.

Because absorption A is a function of intensity I, as the presence ofthe first preselected gas in the gas sample increases, the intensity Iof the beam 12 as it passes through the gas sample decreasesproportionately. This reduced intensity beam 12 then impinges on one ormore photodetectors 52, 64 where it is converted into an electricalsignal 54, 66. This signal 54, 66 is compared to an electrical signal 34from a reference cell 31 (e.g. 50% vol. ¹²CH₄) that includes aphotodetector 32 on which beam 12 impinges without passing through thegas sample.

The operating temperature T_(op) of the light source 14 can then beshifted as follows

$\begin{matrix}{T_{{op}{(2)}} = {T_{{op}{(1)}} + \frac{\Delta \; {nm}}{d\; {\lambda/{dT}}}}} & \left( {{Eq}.\mspace{14mu} 3} \right) \\{{\Delta \; {nm}} = {\lambda_{(1)} - \lambda_{(2)}}} & \left( {{Eq}.\mspace{14mu} 4} \right)\end{matrix}$

where λ is the wavelength corresponding to a frequency of highabsorption for a respective preselected gas. Calibration tables can beused to determine the correct operating temperature of the light sourceneeded to produce the desired wavelength.

For measurement accuracy the operating temperature of light beam 12 canbe controlled within a narrow range. For example, the temperature can bemaintained within 1° C., 0.5° C., 0.1° C., or a similar range, of theselected operating temperature T_(op). This control is accomplishedusing a temperature regulating system 16 that includes a thermoelectriccooler (“TEC”) driver. Similar means to temperature regulating system 16can be applied to control the operating temperature of one or more ofthe photodetectors 32, 52, 62 and increase detection sensitivity for apreselected gas. Thus, depending on the embodiment, one or both of thetemperatures of the light source and the photodetectors may bedynamically adjusted to detect particular gases. This operatingtemperature can be correlated with that of the light source 14. Or,optionally, only the operating temperature of one or more of thephotodetectors 32, 52, 64 is changed with the operating temperature ofthe light source 14 being constant.

In various embodiments, the temperature regulating system 16 can includea TEC driver and/or a heating element to precisely control the operatingtemperature of the light source 14. In addition, some embodiments mayachieve control of the temperature of the light source 14 by regulatingthe amount of current applied to the light source 14, thereby modifyingthe amount of heat generated in the circuitry of the light source 14 byresistive heating. Thus, any reference herein to a heating component mayrefer to a heating element external to a light source and/or the lightsource itself (e.g., such as in the embodiment noted above where thelight source itself can provide resistive heating). In some embodiments,a light source has known temperatures at corresponding known currentlevels. Thus, the system discussed herein may store those relationships(e.g., in a temperature-to-current lookup table) that is usable toadjust the light source to any available temperatures by adjustingcurrent levels driving the light source.

In some embodiments where, a heat control assembly includes a heat sinkhaving cooling fins that are exposed to the stream of sample gas. Inembodiments where the heating element includes an external heatingcomponent, the light source may be mounted in contact with a peltierelement that in turn is in heat conductive relationship with the heatsink. In some embodiments, a thermistor may be included in the heatcontrol assembly for sensing temperature of the heat sink and/or heatingelement itself and sending a control signal to the microprocessor. Thethermistor output may then be used to determine when temperatureadjustments are needed, and initiate such temperature changes using theavailable heating element(s) and/or cooling element(s).

The portion 12A of the beam 12 exits as beam 50. This exit beam 50impinges on a (high sensitivity) photo detector 52. The signal passesthrough an amplifier circuit 56 and an analog-to-digital converter 58that provides a digital signal to microcontroller 42.

Another portion 62 of the intensity of the beam 12A exits and impingeson a (low sensitivity) photo detector 64. The signal passes through anamplifier circuit 68 and an analog-to-digital converter 70 that providesa digital signal to microcontroller 42.

Another portion 12B of light beam 12 does not enter the measurement cellat all. Rather, it is reflected away from the cell by a mirror. Thisportion 12B impinges on a photo detector 32 that provides a signal. Thissignal, which provides a reference signal, is representative of themaximum intensity of the light beam 12. The signal passes through anamplifier circuit 36 and an analog-to-digital converter 38 that providesa reference digital signal to microcontroller 42.

By comparing the intensity of the signal associated with reflected beam12B with the signal associated with bounced back-and-forth beam 12A thatexits as beam 50, the concentration of ¹²CH₄ in the sample gas can bedetermined with great accuracy using microcontroller 42 and detected ata sensitivity down to a few parts per million or even, ideally, to asensitivity of one or less than one part per million. Because themethane found in natural gas contains 1% of isotope 13, if theconcentration of ¹²CH₄ is ≧200 ppm, then discrimination of ¹³CH₄ isachievable at a level of detection of 2 ppm.

Note the use of two separate exit beams 50, 62 to activate photodetectors 52, 64 respectively becomes important where ¹²CH₄ is presentat a relatively high level in the sample gas. At high levels beam 12Acan be, for all practical purposes, completely absorbed before it existsthrough aperture 48 and, therefore, provided insufficient intensity ofthe beam 12A for use in computing the percentage of ¹²CH₄. This problemis overcome by the use of the second exit beam 62 and photo detector 64.Because the second exit beam 62 travels a relatively short distancethrough the gas sample, the attenuation of the beam 62 occurs at a ratethat can provide methane detection even when the percentage of methanein the test gas is many times higher than that which is detectable byphoto detector 52. The use of two separate exit beams 50, 62, one havinga short length light path through the gas sample and the other having along length light path, provides a system wherein the range ofconcentration of methane that can be measured is greatly expanded.

Preferably, light source 14 is not energized by a steady state voltageto produce a steady state light beam 12 but rather pulsed with a sawtooth wave shaped current. Each pulsation of light source 14 generates apulsed light beam 12 that varies in wavelength over a selectedbandwidth. Each current pulse produces light that varies in wavelengthabove and below the wavelength that undergoes the greatest absorption ofthe specific gas the instrument is designed to detect.

Because light source 14 is energized by a particular pulsed currentwaveform, the resultant signals generated by photo detectors 32, 52 and64 are characterized by that particular waveform. Therefore, withinmicrocontroller 42, absorption is detected by electronically dividingthe signal of photo detectors 52 and 64 by the signal of photo detector32. Microcontroller 42 is additionally connected to the temperatureregulating system 16 of the light beam source 14, such that control ofthe temperature of the light beam source 14 can be determined based atleast in part on the results of the absorption detection also carriedout at the microcontroller 42. Methods of controlling and changing thetemperature of the light beam source 14 based on detected absorption atthe microcontroller 42 are described in greater detail below withreference to FIGS. 3 and 5.

Referring now to FIG. 3, an example method of detecting a concentrationof multiple gases using a single cell will be described. The method 300depicted in FIG. 3 can be implemented with the system described abovewith reference to FIG. 1, for example. As discussed further below, theprocess allows the system of FIG. 1 to be dynamically adjusted tomeasure concentration of any gas capable of being detected by infraredabsorption. The process of FIG. 3 may be performed by microcontroller 42and/or any other combination of particularly programmed hardware,firmware, and/or software. Depending on the embodiment, the method ofFIG. 3 may include additional or fewer blocks and/or the blocks may beperformed in a different order than is illustrated.

Method 300 begins at block 305 as a light source is energized at a firstselected temperature T_(op(1)). As described above, the temperatureT_(op(1)) can be selected based on a known operating temperature of thelight source that will produce light at a wavelength corresponding to anabsorption peak of a first gas to be detected. At block 310, the lightbeam produced by the light source is split and passed through a gassample. After the light beam is passed through the gas sample, themethod 300 continues to block 315.

At block 315, the concentration level C₍₁₎ of the first gas isdetermined within the gas sample. Determination of the concentration ofthe first gas within the gas sample can be based on analyzing a signalproduced by one or more photodetectors and/or other circuitry incommunication with the photodetectors as described above with referenceto FIGS. 1 and 2. In some aspects, the concentration may be determinedin units of parts per million (ppm), parts per billion (ppb), percent byvolume, or the like. When the concentration level of the first gas hasbeen determined, the method 300 continues to block 320.

At block 320, the concentration level C₍₁₎ of the first gas within thegas sample is compared to a predetermined threshold or limit Limit₍₁₎.In some embodiments, Limit₍₁₎ can be a threshold expressed in units ofconcentration, such as ppm, and the calculated concentration level C₍₁₎can be compared to the threshold Limit₍₁₎. In other embodiments,Limit₍₁₎ can be a threshold expressed in units of absorbance or othercharacteristic of an analog or digital signal. In such embodiments, theanalog signal generated by the one or more photodetectors, or a digitalsignal generated at an analog-to-digital converter based on the analogsignal, may be compared directly to the threshold Limit₍₁₎ withoutrequiring conversion to a concentration value C₍₁₎. Once theconcentration or absorbance-based signal indicative of concentration iscompared to Limit₍₁₎, a microprocessor or other circuitry of thedetection system can determine whether the concentration of the firstgas within the gas sample is greater than or equal to a preselecteddetection threshold. If the detection system determines that theconcentration of the first gas is greater than or equal to thepreselected detection threshold, the method 300 continues to block 325.If the detection system determines that the concentration of the firstgas is not greater than or equal to the preselected detection threshold,the method 300 continues to block 330.

At block 325, if a concentration of the first gas has been detected thatis at least equal to the predetermined threshold, the level ofconcentration can be reported. For example, the detection system mayprovide a graphic, audible, or other indication of a detection of thefirst gas, such as on a display of the detection system. In anotherexample, reporting the level may include recording a concentration valuein a memory unit of the display system and may or may not include anotification to a user of the system. After the detected concentrationlevel is reported, the method 300 continues to block 330. In someembodiments, the comparison of block 320 and reporting of block 325 isnot performed by the method. For example, the current concentration ofgas may be displayed to the user without comparing to a presetthreshold.

In some embodiments, the system is configured to provide alerts to oneor more users, such as when a predetermined concentration of a gas isdetected. For example, a notification may be automatically communicated,such as in real time as they are detected by the system (which may bestationary or attached to a self-driving vehicle, for example) to asupervising user, such as a technician that is responsible foridentifying/confirming gas leaks. Such communications may beautomatically transmitted to the entity in one or more modes ofcommunication, such as, for example, electronic mail, text messaging,and regular postal mail, to name a few. In certain modes ofcommunication to the entity, the communication may be configured toautomatically operate on the entity's electronic device. For example,the entity's mobile device may, upon receipt of the transmittedcommunication, activate a software application installed on the entity'smobile device to deliver the communication to the entity (e.g., a SMSviewer or application may automatically display information from thecommunication when received by the device or when the device isconnected to the internet). Alternatively, the communication mayactivate a web browser and access a web site to present thecommunication to the entity. In another example, a communication may betransmitted to an entity's email account and, when received,automatically cause the entity's device, such as a computer, tablet, orthe like, to display the transmitted communication or a link to take theentity to a webpage with additional account information.

At block 330, after the method 300 has either reported a concentrationat block 325 or determined that the concentration is less than thethreshold Limit₍₁₎ at block 320, the method 300 determines whether tocontinue sampling to detect the first gas within the gas sample. Thedetermination to continue sampling for the first gas or not to continuesampling for the first gas can be based at least in part on the outcomeof the comparison of block 320. For example, if the concentration wasdetermined to be less than the threshold Limit₍₁₎ at block 320, themethod 300 may continue sampling to detect the first gas within thesample gas. If the concentration was determined to be greater than thethreshold Limit₍₁₎ at block 320, the method 300 may determine thatadditional sampling for the first gas should not be done. In certainembodiments, the method 300 may determine that additional sampling forthe first gas is required after detecting a concentration greater thanthe threshold Limit₍₁₎ to enhance the accuracy of the detection of thefirst gas. If the method determines that continued sampling for thefirst gas is to be done, the method 300 returns to block 315 while thelight source remains energized at T_(op(1)) to continue sampling. Ifsampling to detect the first gas is not to be continued, the method 300continues to block 335. In an exemplary embodiment, a detection systemmay be configured to continuously and/or repeatedly sample for the firstgas by determining “yes” at block 330 each time it is determined atblock 320 that the concentration of the first gas is less than thethreshold, until a concentration above the threshold is detected. Once aconcentration above the threshold is detected, the exemplary systemdetermines “no” at block 330 and continues to block 335.

At block 335, the light source is energized to an operating temperatureequal to T_(op(2)). Depending on the embodiment, the light source maycontinue emitting light as the temperature of the light source ischanged or may be turned off during the temperature transition. Once thelight source is energized at T_(op(2)), the beam continues to passthrough the sample gas at block 340. At block 345, the concentrationlevel C₍₂₎ of the second gas is determined within the gas sample.Determination of the concentration of the second gas within the gassample can similarly be based on analyzing a signal produced by the oneor more photodetectors and/or other circuitry in communication with theone or more photodetectors as described above with reference to FIGS. 1and 2. When the concentration level of the second gas has beendetermined, the method 300 continues to block 350.

At block 350, the concentration level C₍₂₎ of the second gas within thegas sample is compared to a predetermined threshold or limit for thesecond gas Limit₍₂₎. Like Limit₍₁₎, Limit₍₂₎ can be a thresholdexpressed in units of concentration, such as ppm, and the calculatedconcentration level C₍₂₎ can be compared to the threshold Limit₍₂₎. Inother embodiments, Limit₍₂₎ can be a threshold expressed in units ofabsorbance or other characteristic of an analog or digital signal. Insuch embodiments, the analog signal generated by the one or morephotodetectors, or a digital signal generated at an analog-to-digitalconverter based on the analog signal, may be compared directly to thethreshold Limit₍₂₎ without requiring conversion to a concentration valueC₍₂₎. Once the concentration or absorbance-based signal indicative ofconcentration is compared to Limit₍₂₎, a microprocessor or othercircuitry of the detection system can determine whether theconcentration of the second gas within the gas sample is greater than orequal to the preselected detection threshold. If the detection systemdetermines that the concentration of the second gas is greater than orequal to the preselected detection threshold, the method 300 continuesto block 355. If the detection system determines that the concentrationof the second gas is not greater than or equal to the preselecteddetection threshold, the method 300 continues to block 360.

At block 355, if a concentration of the second gas has been detectedthat is at least equal to the predetermined threshold for the secondgas, the level of concentration can be reported. For example, thedetection system may provide a graphic indication of a detection of thesecond gas, such as on a display of the detection system. In anotherexample, reporting the level may include recording a concentration valuein a memory unit of the display system and may or may not include anotification to a user of the system. After the detected concentrationlevel is reported, the method 300 continues to block 360.

At block 360, after the method 300 has either reported a concentrationat block 355 or determined that the concentration of the second gas isless than the threshold Limit₍₂₎ at block 350, the method 300 determineswhether to continue sampling to detect the second gas within the gassample. Similar to the determination to continue sampling for the firstgas at block 330, the determination to continue sampling for the secondgas or not to continue sampling for the second gas can be based at leastin part on the outcome of the comparison of block 350. For example, ifthe concentration of the second gas was determined to be less than thethreshold Limit₍₂₎ at block 350, the method 300 may continue sampling todetect the second gas within the sample gas. If the concentration wasdetermined to be greater than the threshold Limit₍₂₎ at block 350, themethod 300 may determine that additional sampling for the second gas isrequired to enhance the accuracy of the detection of the second gas. Inother aspects, the method 300 may determine that the determinedconcentration of the second gas is reliable and determine thatadditional sampling for the second gas should not be done. If the methoddetermines that continued sampling for the second gas is to be done, themethod 300 returns to block 345 while the light source remains energizedat T_(op(2)) to continue sampling. If sampling to detect the second gasis not to be continued, the method 300 can return to block 305 to beginthe detection process again.

Although the method 300 is described generally in terms of repeatedlysampling to detect a first gas and transitioning to detect a second gasonce the first gas is detected, other embodiments may be configured toalternate sampling for a first gas and a second gas without requiring afirst gas to be detected to initiate the transition. For example, incertain implementations, the method 300 can sample to detect a first gasfor a set time period, such as 1 second, 3 seconds, 5 seconds, 10seconds, or the like, then proceed to sample for the second gas for asimilar time period, such as 1 second, 3 seconds, 5 seconds, 10 secondsor the like, then sample again for the first gas. This cycle may repeatindefinitely. Each transition between sampling for the first and thesecond gas can be performed based on the expiration of the predeterminedtime period, independent of whether a detectable concentration of eithergas was detected during the preceding time period.

In certain embodiments of the gas detection systems discussed herein,the systems may perform a method including moving a stream of sample gasfrom the environment through a confined testing area such as cell 10within a detecting instrument; energizing a light source 14 at a firstoperating temperature to produce a first light beam 12 at a frequencythat corresponds to a high degree of absorption by a first preselectedgas; splitting the first light beam 12 into three components; passing afirst component of the first light beam 12 to a first photo detector 32for providing a first electrical signal indicative of the intensity ofthe first light beam 12; passing a second component of the first lightbeam 12 multiple times through the confined testing area and then to asecond photo detector 52 for providing a second electrical signalindicative of a concentration measurement corresponding to a lowerconcentration level; passing a third component of the first light beam12 over a reduced length exit beam path 62 through the confined testingarea and then to a third photo detector 64 for providing a thirdelectrical signal indicative of a concentration measurementcorresponding to a higher concentration level; using the first, second,and third electrical signals for determining the concentration level ofthe first preselected gas in the stream of sample gas; energizing thelight source 14 at a second open component of the second light beam 12to the first photo detector 32 for providing a first electrical signalindicative of the intensity of the second light beam; passing a secondcomponent of the second light beam 12 multiple times through theconfined testing area and then to the second photo detector 52 forproviding a second electrical signal indicative of a concentrationmeasurement corresponding to a lower concentration level; passing athird component of the second light beam 12 over a reduced length path62 through the confined testing area and then to the third photodetector 64 for providing a third electrical signal indicative of aconcentration measurement corresponding to a higher concentration level;and using the first, second, and third electrical signals fordetermining the concentration level of the second preselected gas in thestream of sample gas.

Referring jointly to FIGS. 4 and 5, an example method of discriminatingbetween a first and second gas will be described. In some embodiments,and by way of example only, the system and method can be used todiscriminate between methane originating from a natural gas source andfrom a biogas source. Natural gas includes 82% to 95% of methane, with99% of this methane being isotope C12 (“¹²CH₄”) and 1% being isotope C13(“¹³CH₄”). The methane found in biogas only includes isotope C12.Isotope C12 absorbs in near infrared in 1650.9 nm and 1653.7 nm. IsotopeC13 absorbs in 1650.4 nm or 1653.1 nm. The infrared absorption spectra400 in FIG. 4 depicts absorption of infrared by ¹²CH₄ and ¹³CH₄ between1650.1 nm and 1651.1 nm. As shown in the spectra 400, ¹²CH₄ has anabsorption peak 405 at approximately 1650.9 nm, while ¹³CH₄ has anabsorption peak 410 at approximately 1650.4 nm. Accordingly, detectionof absorption when a sample gas is exposed to infrared light having awavelength of 1650.9 nm indicates the presence of ¹²CH₄, and the amountof absorption can determine the concentration of ¹²CH₄ within thesample. Similarly, detection of absorption when a sample gas is exposedto infrared light having a wavelength of 1650.4 nm indicates thepresence of ¹³CH₄, and the amount of absorption can determine theconcentration of ¹³CH₄ within the sample.

Accordingly, the example method 500 depicted in FIG. 5 can be used todetect methane and determine if the methane is from a natural gas sourceor a biogas source. Reference to components of a detection systemthroughout the description of the method 500 in FIG. 5 are withreference to the components as depicted in FIG. 1. To detect ¹²CH₄, thelight beam source 14 is set to operate at T_(op)=T_(op(12CH4)) at block505 to produce a beam 12 having a wavelength λ that corresponds to highdegree of absorption by ¹²CH₄. By way of example only, the light beamsource 14 used in certain embodiments may be configured to produce abeam at approximately 1650.9 nm when operating at 25° C. In variousembodiments, the appropriate operating temperature to produce a 1650.9nm light beam can be determined for a particular light beam source basedon the thermal and/or electrical properties of the light beam source.Beam 12 then exits the cell 10 and is measured by photodetectors 52, 64.In some embodiments, the measurement time can be 3 seconds, 5 seconds,10 seconds, or similar. Once the beam 12 is measured by photodetectors52, 64, the method 500 continues to block 510.

At block 510, the method 500 determines if the first gas is present in aconcentration greater than or equal to a predetermined concentrationthreshold. In the example embodiment depicted, the threshold can be 200ppm. If less than 200 ppm of ¹²CH₄ is detected (or some otherpredetermined concentration threshold), the method 500 proceeds toterminate at block 515 without performing a discrimination step. If 200ppm or more of ¹²CH₄ is detected, the method proceeds to determine atblock 525 that a sufficient concentration of methane is present in thesample gas to determine that a leak exits and/or to permitdiscrimination between natural gas and biogas. The threshold level of¹²CH₄ can be determined, for example, based on a known limit ofdetection (“LOD”) of the secondary gas to be detected. In one example,it may be known that the concentration of ¹³CH₄ in natural gas isexpected to be approximately 1% of the ¹²CH₄ concentration, and thedetector may have a limit of detection of approximately 2 ppm.Accordingly, the threshold for ¹²CH₄ can be determined to be 200 ppm,such that ¹³CH₄, if present, can be detected using the detector. In suchsystems, a concentration below 200 ppm of ¹²CH₄ likely could not bereliably evaluated for the presence of ¹³CH₄ because the ¹³CH₄concentration, if present, is expected to be less than 2 ppm.

At block 530, the light beam source 14 shifts to operate atT_(op(13CH4)), with the beam 12 having a wavelength λ that correspondsto high degree of absorption by ¹³CH₄. The particular shifting intemperature of the light beam source 14 to achieve the wavelength λ maybe determined based on one or more algorithms and/or calibration tables.In a non-limiting example, if the light beam source described aboveproduces a beam at 1650.9 nm when operating at 25° C., and dλ/dT of thelight beam source is 0.1 nm/° C., the operating temperaturecorresponding to a beam at 1650.4 nm can be approximately 19-20° C.Preferably, the transition from T_(op(12CH4)) to T_(op(13CH4)) isrelatively short, such as within 10 seconds, 5 seconds, or the like.Beam 12 again exits the cell 10 and is again measured by photodetectors52, 62. Once the beam 12 is measured by photodetectors 52, 64, themethod 500 continues to block 535.

At block 535, the method 500 determines if the second gas is present ina concentration greater than or equal to a second predeterminedconcentration threshold. In the example embodiment depicted, the secondthreshold can be 2 ppm. If 2 ppm or more (or some other predeterminedconcentration threshold) of ¹³CH₄ is detected, the method 500 terminatesat block 540, where it is determined that the sample gas is from anatural gas source. If a concentration less than 2 ppm is detected, orif ¹³CH₄ is not detected at all, the method 500 terminates at block 550,where it is determined that the sample gas is from a biogas source. Invarious embodiments, the threshold for ¹²CH₄ can be greater or less than200 ppm, and may be based at least in part on the ability of the systemto detect low concentrations of a gas. For example, an initial thresholdof 200 ppm may be selected where the system can reliably detect aninfrared absorbing gas at 2 ppm and where the second gas or isotopecomprises up to 1% of the gas.

After determining the source of the sample gas at block 540 or block550, the method 500 can further include sending a notification. Forexample, a visual or audio indication of the source of the sample gascan be provided to a user of an analyzer or other apparatus performingthe method 500 (e.g., a mobile device or display in communication withthe analyzer and/or a remote computing device). In the exampleapplication of a gas company (or other entity) inspecting itsinfrastructure for leaks, a detection of methane, accompanied by anotification that the methane is from a biogas source rather than anatural gas source, can indicate that the detection of methane is notindicative of a natural gas leak. Similarly, a detection of methaneaccompanied by a notification that the methane is from a natural gassource can indicate that the detection of methane likely is indicativeof a natural gas leak. Thus, the gas company can avoid wasting resourcessending additional equipment and/or technicians to the site of themethane detection in the absence of a natural gas leak.

In another example, notifications may further include an indication thata first target gas has been detected, but at a concentration below thethreshold for detecting the second target gas. In the example of anatural gas leak survey, a user can be notified of a “hit,” indicatingthat methane has been detected, but at a level lower than the naturalgas-biogas discrimination threshold (e.g., 200 ppm of ¹²CH₄ in theexample of FIG. 5). Based on such notification, the user can be promptedto continue sampling in the area, as there may be a location nearby(e.g., closer to the source of the detected gas) where the concentrationis higher and may exceed the threshold. Based on the notification theuser can sample in additional locations within the vicinity of theinitial notification until the analyzer detects a concentration of thefirst target gas above the predetermined threshold, samples for thesecond target gas, and notifies the user as to the outcome of thediscrimination process. In some embodiments, a mobile analyzer mayinclude a display that is continuously updated with the concentrationlevel of the first gas, such as in relationship to the concentrationlevel needed to discriminate between one or more constituent gases.

The embodiments described above are examples of the system and method.The following claims define the scope of the invention and include thefull range of equivalents to which the recited elements of the claimsare entitled.

The foregoing description details certain embodiments of the systems,devices, and methods disclosed herein. It will be appreciated, however,that no matter how detailed the foregoing appears in text, the devicesand methods can be practiced in many ways. As is also stated above, itshould be noted that the use of particular terminology when describingcertain features or aspects of the invention should not be taken toimply that the terminology is being re-defined herein to be restrictedto including any specific characteristics of the features or aspects ofthe technology with which that terminology is associated. The scope ofthe disclosure should therefore be construed in accordance with theappended claims and any equivalents thereof.

With respect to the use of any plural and/or singular terms herein,those having skill in the art can translate from the plural to thesingular and/or from the singular to the plural as is appropriate to thecontext and/or application. The various singular/plural permutations maybe expressly set forth herein for sake of clarity.

In general, the microprocessors and/or computing discussed herein mayeach include on or more “components” or “modules,” wherein generallyrefer to logic embodied in hardware or firmware, or to a collection ofsoftware instructions, possibly having entry and exit points, written ina programming language, such as, for example, Java, Lua, C or C++. Asoftware module can be compiled and linked into an executable program,installed in a dynamic link library, or can be written in an interpretedprogramming language such as, for example, BASIC, Perl, or Python. Itwill be appreciated that software modules can be callable from othermodules or from themselves, and/or can be invoked in response todetected events or interrupts. Software modules configured for executionon computing devices can be provided on a computer readable medium, suchas a compact disc, digital video disc, flash drive, magnetic disc, orany other tangible medium, or as a digital download (and can beoriginally stored in a compressed or installable format that requiresinstallation, decompression or decryption prior to execution). Suchsoftware code can be stored, partially or fully, on a memory device ofthe executing computing device, for execution by the computing device.Software instructions can be embedded in firmware, such as an EPROM. Itwill be further appreciated that hardware modules can be comprised ofconnected logic units, such as gates and flip-flops, and/or can becomprised of programmable units, such as programmable gate arrays orprocessors. The modules or computing device functionality describedherein are preferably implemented as software modules, but can berepresented in hardware or firmware. Generally, the modules describedherein refer to logical modules that can be combined with other modulesor divided into sub-modules despite their physical organization orstorage.

The term “non-transitory media,” and similar terms, as used hereinrefers to any media that store data and/or instructions that cause amachine to operate in a specific fashion. Such non-transitory media cancomprise non-volatile media and/or volatile media. Non-volatile mediaincludes, for example, optical or magnetic disks, such as storagedevice. Volatile media includes dynamic memory, such as main memory.Common forms of non-transitory media include, for example, a floppydisk, a flexible disk, hard disk, solid state drive, magnetic tape, orany other magnetic data storage medium, a CD-ROM, any other optical datastorage medium, any physical medium with patterns of holes, a RAM, aPROM, and EPROM, a FLASH-EPROM, NVRAM, any other memory chip orcartridge, and networked versions of the same.

It is noted that the examples may be described as a process. Althoughthe operations may be described as a sequential process, many of theoperations can be performed in parallel, or concurrently, and theprocess can be repeated. In addition, the order of the operations may berearranged. A process is terminated when its operations are completed. Aprocess may correspond to a method, a function, a procedure, asubroutine, a subprogram, etc.

The previous description of the disclosed implementations is provided toenable any person skilled in the art to make or use the presentdisclosed process and system. Various modifications to theseimplementations will be readily apparent to those skilled in the art,and the generic principles defined herein may be applied to otherimplementations without departing from the spirit or scope of thedisclosed process and system. Thus, the present disclosed process andsystem is not intended to be limited to the implementations shown hereinbut is to be accorded the widest scope consistent with the principlesand novel features disclosed herein.

What is claimed is:
 1. A method of measuring a concentration in anenvironment of at least a first preselected gas and a second preselectedgas, the method comprising: determining a temperature of a light sourceof a detection system; based on the determined temperature, initiatingactivation of a cooling or a heating component associated with the lightsource to adjust the temperature to a predetermined first operatingtemperature, wherein the first operating temperature is selected toproduce a light beam from the light source at a first preselectedwavelength for absorption by the first preselected gas; when thetemperature of the light source has reached the first operatingtemperature, accessing measurement data from an optical detector,wherein with the light source at the predetermined first temperature thedetection system is configured to measure a first absorption of thelight beam at the first preselected wavelength to provide an indicationof a concentration of the first preselected gas within the sample gas;initiating activation of a cooling or heating component associated withthe light source to adjust the temperature to a predetermined secondoperating temperature, wherein the second operating temperature isselected to produce a light beam from the light source at a secondpreselected wavelength for absorption by the second preselected gas; andwhen the temperature of the light source has reached the secondoperating temperature, accessing measurement data from the opticaldetector, wherein with the light source at the predetermined secondtemperature the detection system is configured to measure a secondabsorption of the light beam at the second preselected wavelength toprovide an indication of a concentration of the second preselected gaswithin the sample gas.
 2. The method of claim 1, wherein at least one ofthe first and second preselected gases is selected from the groupconsisting of methane (CH4), ethane (C2H6), propane (C3H8), butane(C4H10), oxygen (O2), hydrogen (H2), nitrogen (N), water (H2O), hydrogenfluoride (HF), hydrogen chloride (HCl), hydrogen bromide (HBr), hydrogensulfide (H2S), ammoniac (NH3), ammonia (NH4), carbon monoxide (CO),carbon dioxide (CO2), nitrogen monoxide (NO), nitrogen dioxide (NO2),sulfur hexafluoride (SF6), tetrahydrothiophene (C4H8S), and tert-butylmercaptan (C4H10S).
 3. The method of claim 1, wherein the secondpreselected gas is an isotopologue of the first preselected gas.
 4. Themethod of claim 3, wherein the first preselected gas and the secondpreselected gas are isotopologues of methane.
 5. The method of claim 1,wherein the cooling or heating component is configured to adjust thetemperature of the light source between the first operating temperatureand the second operating temperature in less than 10 seconds.
 6. Themethod of claim 1, wherein the light source is a laser diode.
 7. Themethod of claim 1, wherein the light source is a light emitting diode.8. The method of claim 1, wherein the optical detector is aphotodetector.
 9. The method of claim 8, further comprising determininga temperature of the photodetector and initiating a heating or coolingcomponent associated with the photodetector to adjust the temperature ofthe photodetector to an operating temperature of the photodetector. 10.The method of claim 9, wherein the operating temperature of thephotodetector is controlled based on at least one of the first andsecond operating temperatures.
 11. The method of claim 1, wherein thedetecting instrument further comprises a multi-pass cell.
 12. The methodof claim 1, wherein the temperature of the light source is adjusted tothe second operating temperature based at least in part on theindication of the concentration of the first preselected gas.
 13. Themethod of claim 12, wherein the temperature of the light source isadjusted to the second operating temperature responsive to theindication of the concentration of the first preselected gas exceeding apredetermined threshold.
 14. A method of measuring a concentration in anenvironment of at least a first preselected gas and a second preselectedgas, the method comprising: continuously moving a stream of a sample gasfrom the environment through a confined testing area within a detectinginstrument; energizing a light source of the detecting instrument toproduce a light beam at a wavelength that corresponds to an absorptionline of a gas; and energizing a photodetector at a first operatingtemperature to detect absorption of the light beam by the firstpreselected gas.
 15. The method of claim 14 further comprising:energizing the photodetector at a second operating temperature to detectabsorption of the light beam by the second preselected gas; andmeasuring the absorption of the light beam to provide an indication of aconcentration of the second preselected gas at the preselectedwavelength.
 16. The method of claim 14 further comprising energizing thelight source at a first operating temperature to produce a light beam ata preselected wavelength for absorption by the first preselected gas.17. The method of claim 14 further comprising energizing the lightsource at a second operating temperature to produce a light beam at apreselected wavelength for absorption by the second preselected gas. 18.A method of measuring a concentration in an environment of a preselectedgas, the method comprising: continuously moving a stream of a sample gasfrom the environment through a confined testing area within a detectinginstrument; energizing a light source of the detecting instrument toproduce a light beam at a wavelength that corresponds to an absorptionline of a reference gas; energizing the light source at a firstoperating temperature to produce a light beam at a preselectedwavelength for absorption by a first preselected gas, the preselectedwavelength being a different wavelength than that the wavelengthcorresponding to the absorption line of the reference gas; and measuringthe absorption of the light beam to provide an indication of aconcentration of the first preselected gas at the preselectedwavelength.
 19. The method of claim 18 further comprising: energizingthe light source at a second operating temperature to produce a lightbeam at a preselected wavelength for absorption by a second preselectedgas; and measuring the absorption of the light beam to provide anindication of a concentration of the second preselected gas at thepreselected wavelength.
 20. A system for measuring concentration of atleast a first preselected gas and a second preselected gas, the systemcomprising: a light source configured to produce a light beam having awavelength at least partially dependent upon a temperature of the lightsource, wherein a first operating temperature of the light source isselected to produce a light beam at a first preselected wavelength forabsorption by the first preselected gas, and wherein a second operatingtemperature of the light source is selected to produce a light beam at asecond preselected wavelength for absorption by the second preselectedgas; an optical detector configured to measure an absorption of thelight beam; a temperature sensor configured to detect the temperature ofthe light source; a temperature control element configured to adjust thetemperature of the light source based on a current traveling through atleast a portion of the temperature control element; and processingcircuitry in communication with the optical detector, the temperaturesensor, and the temperature control element, the processing circuitryconfigured to initiate activation of the temperature control elementbased at least in part on at least one of the absorption of the lightbeam and the temperature of the light source.
 21. The system of claim20, wherein the light source comprises a laser diode.
 22. The system ofclaim 20, wherein the temperature control element comprises athermoelectric cooler.
 23. The system of claim 20, wherein thetemperature control element comprises a heating element.
 24. The systemof claim 23, wherein the heating element comprises internal circuitry ofthe light source.
 25. The system of claim 20, wherein the processingcircuitry is configured to initiate activation of the temperaturecontrol element to adjust the temperature from the first operatingtemperature to the second operating temperature based at least in parton the absorption of the light beam measured at the optical detectorexceeding a predetermined threshold.
 26. The system of claim 20, furthercomprising a multi-pass cell, wherein an optical path of the light beambetween the light source and the optical detector passes through themulti-pass cell.